You must purchase Studio One 3 Professional or the VST, AU, and ReWire support plug-in with Studio One 3 Artist in order to load 3rd-party plug-ins. There is not a comprehensive list that illustrates all plug-ins that are compatible with Studio One as this list would constantly be changing. It is up to the manufacturer of a plug-in to provide compatibility with Studio One, should they choose to do so. Studio One supports 3rd-party VST 2 plug-ins, VST3 plug-ins, and Audio Units. It is best to contact the manufacturer of a plug-in and ask if the plug-in is compatible with Studio One 3.
Here is a link to UVI's web site for the Orchestral Suite's product page.
If you scroll down to the bottom of that page, you will see all of the DAW's that they have tested with and certified. They are listing the plugin as compatible with Studio One version 2 and above.